The present invention relates to slip-joint pliers of the type generally referred to as combination pliers, because of their included ability to cut wire.
In the standard configuration the pliers consist of two handle members, adjustable to two jaw positions by means of a shiftable bolt of one member pivoting inside a slot of the other member. The threaded, for a nut, shoulder bolt has a shoulder portion that is flattened on two opposite sides.
The length of the portion is slightly less than the combined thickness of the two members in the pivot area. A double-D shaped hole in one member receives the bolt and rotation is prevented. The slot is shaped like and open, on center, figure 8 that permits the flattened section to slip through the narrowed down slot. In this manner two pivot centers are established, some short distance apart.
Applying pressure on the plier handles forces the pivot pin against the minimal material at the narrowed passage of the slot in the direction of the other end of the slot. Push combined with torque result in wear and enlargement in this area and binding of the pin is an early sign of the wearing process. Breakthrough of the pin is postponed by the selection of higher grade forging materials. The pivot pin proposed in my new pivot geometry is round without flats, thereby stronger, and bears against the ends of normally shaped slots and thus increases bearing areas by 300 percent. The now slotted plier members are identical and consequently favourably effect factory assembly, staging, part movement, inventory, forging dies, single part tooling (holding fixtures), identical and simplified punches that will have longer life if the tool material is lowered in hardness, which is now made possible by the increase in pin bearing surfaces.
The standard pivot geometry makes the tool non-symmetrical and for that reason inherits three drawbacks that most people have learned to live with, because a solution is entirely not obvious.
The first drawback is that in the widest adjusted position, from now on called Position 2, the tips of the jaws will not come together so that pinching is not possible here.
The second drawback is that wire cannot be cut in Position 2 because the cutters don't line up.
The third drawback is that all attempts known to me, to make the pliers spring-loaded for improved operator's grip and control have been awkward, cumbersome and non-cooperative to satisfy both adjusted positions equally.
One notable exception is revealed in U.S. Pat. No. 4,669,340 which only suffers from increased cost due to the need for machining the forged members, each one of which in a different way.
The present invention is intended to overcome the aforementioned limitations of the prior art by providing a pivot geometry wherein the pivot remains centered for both adjusted positions and which then makes the construction and installation of a handle/jaw assist spring a viable proposition.